Mems mirror driven by dual pulse drive signal

ABSTRACT

Mirror control circuitry operates to control a movable mirror. The mirror control circuitry includes drive circuitry for providing a drive signal to the movable mirror, and a processor. The processor causes the drive circuitry to generate the drive signal so as to have pulses with leading edges occurring an offset period of time after a maximum opening angle of the movable mirror and trailing edges occurring an offset period of time before a zero crossing of the movable mirror. The processor may sample a mirror sense signal from the movable mirror at times at which a derivative of capacitance of the movable mirror with respect to time is zero, and then perform an action based upon the samples.

RELATED APPLICATION

This is a divisional of U.S. patent application Ser. No. 15/722,444,filed on Oct. 2, 2017, the contents of which are incorporated byreference to the maximum extent allowable under the law.

TECHNICAL FIELD

This disclosure relates to a technique for driving an oscillating mirrorwith a drive signal that produces at least two drive pulses per eachperiod of mirror oscillation.

BACKGROUND

Certain devices such as wafer defect scanners, laser printers, augmentedreality devices, document scanners, projectors and the like often employa laser beam that scans across a surface in a straight or curved linepath. These devices employ tilting mirrors to deflect the beam toperform the scanning. These tilting mirrors may be, or may include,Micro Electro Mechanical Systems (“MEMS”) devices. The actuation ofmirrors used in MEMS devices, referred to herein as MEMS mirrors, can bevia the electromagnetic, electrostatic, piezoelectric, andthermoelectric effects, depending on application.

One type of common MEMS mirror includes a stator and a rotor, with therotor or structures carried by the rotor being reflective. The statorand/or rotor are driven with a drive signal which results in the rotoroscillating with respect to the stator, thereby changing the angle ofreflectance of an incident light beam on the rotor. By oscillating therotor between two orientations, an opening angle of the mirror isdefined, and scanning of the light beam across the surface isaccomplished.

Current control schemes for such a MEMS mirror involve the use of adrive signal with a single pulse per each period of mirror oscillation.A single pulse is utilized so as to permit adequate time for sampling ofan output signal from the MEMS mirror for use in a control loop.

However, the use of a single pulse brings with it certain drawbacks. Forexample, in order to achieve a given opening angle, the magnitude of thevoltage of the mirror drive signal may be required to be relativelyhigh, and the generation of such high voltages in a portable electronicdevice may prove burdensome. In addition, the use of a single pulse andthe accompanying high voltage may result in spurious drive modes, whichis also undesirable.

Therefore, there is a need for new control schemes for MEMS mirrors thatovercome these drawbacks.

SUMMARY

Disclosed herein is a device including mirror control circuitry forcontrolling a movable mirror. The mirror control circuitry includesdrive circuitry for providing a drive signal to the movable mirror, anda processor. The processor is configured to cause the drive circuitry togenerate the drive signal so as to have pulses associated with times atwhich a derivative of a capacitance of the movable mirror with respectto time is zero.

The association between the pulses and the time at which the derivativeof the capacitance of the movable mirror with respect to time is zeromay be that a rising edge of each pulse occurs an offset period of timeafter each time at which the derivative of capacitance of the movablemirror with respect to time is zero but an opening angle of the movablemirror is nonzero, and that a falling edge of each pulse occurs anoffset period of time before each time at which the opening angle of themovable mirror is zero.

The pulses of the drive signal may be generated so as to be trapezoidalin shape.

The processor may be further configured to receive a mirror sense signalfrom the movable mirror, take first and second samples of the mirrorsense signal, both samples being taken between pulses of the drivesignal, determine at least one property of the movable mirror as afunction of the first and second samples, and perform an action basedupon the determined at least one property.

The determined at least one property may be the opening angle of themovable mirror, and the action performed may be to adjust the drivecircuitry such that the opening angle matches a desired opening angle.

The determined at least one property may be that the movable mirror hasfailed, and wherein the action performed may be to generate a flagindicating that the mirror has failed.

The processor may be configured to receive a mirror sense signal fromthe movable mirror, take a first sample of the mirror sense signal at azero crossing of the opening angle of the movable mirror, take a secondsample of the mirror sense signal at a next occurrence of a time atwhich the derivative of the capacitance of the movable mirror withrespect to time is zero, and perform an action based upon the determinedat least one property.

The processor may cause the drive circuitry to generate the drive signalso as to have the pulses transition from deasserted to asserted at anoffset period of time after each time at which the derivative of thecapacitance of the movable mirror with respect to time is zero and theopening angle of the movable mirror is nonzero.

The times at which the derivative of opening angle of the movable mirrorwith respect to time is zero and the opening angle of the movable mirroris nonzero represent maximums or minimums of the opening angle of themovable mirror.

The movable mirror may be an oscillating micromirror.

Also disclosed herein is a method of driving a movable mirror includinggenerating a drive signal for the movable mirror so as to have arespective different pulse generated an offset period of time after eachtime at which an opening angle of the movable mirror is at a maximum orminimum, sampling a mirror sense signal from the movable mirror at leastonce between pulses of the drive signal (or sampling the mirror sensesignal twice per each period of the drive signal), and performing atleast one action as a function of the sampled mirror sense signal.

The drive signal may be generated so as to have a respective pulsetransition from deasserted to asserted an offset period of time aftereach time at which the opening angle of the movable mirror is at amaximum or a minimum.

The method may include determining the phase between the mirror sensesignal and the drive signal, and the action performed may be to adjustthe drive signal such that the phase angle matches a desired phase. Thedesired phase may result in an opening angle of the movable mirrorreaching a maximal, or close to maximal, opening angle. The adjustmentof the drive signal may be an adjustment of the frequency of the drivesignal to a frequency matching, or close to, the resonance frequency ofthe movable mirror.

The method may include determining whether the movable mirror has failedas a function of the sampled mirror sense signal, and the actionperformed may be to generate a flag indicating that the mirror hasfailed.

Also disclosed herein is a device including mirror control circuitry forcontrolling a movable mirror. The mirror control circuitry includesdrive circuitry for providing a drive signal to the movable mirror, anda processor configured to cause the drive circuitry to generate thedrive signal so as to have a frequency that is twice a frequency ofoscillation of the movable mirror but does not have pulses occurring attimes at which a derivative of capacitance of the movable mirror withrespect to time is zero.

The processor may be further configured to receive a mirror sense signalfrom the movable mirror, and take first and second samples of the mirrorsense signal at next two occurrences of the derivative of capacitance ofthe movable mirror with respect to time being zero. In some cases, thefirst and second samples may instead be taken during a single mirrorcycle, or during a single period of the mirror sense signal.

Further disclosed herein is a device including mirror control circuitryfor controlling an oscillating mirror. The mirror control circuitry mayinclude drive circuitry for providing a drive signal to the oscillatingmirror, and a processor configured to cause the drive circuitry togenerate the drive signal so as to have a duty cycle that is less thanone quarter of a period of oscillation of the oscillating mirror and haspulses with leading edges offset from a maximum opening angle of theoscillating mirror and trailing edges offset from a zero crossing of theopening angle of the oscillating mirror.

The processor may be further configured to receive a mirror sense signalfrom the oscillating mirror, and take first and second samples of themirror sense signal at next two occurrences of the derivative ofcapacitance of the oscillating mirror with respect to time being zero.In some cases, the first and second samples may instead be taken duringa single mirror cycle, or during a single period of the mirror sensesignal.

Another method disclosed herein includes generating a drive signal foran oscillating mirror, with the drive signal being generated to have aduty cycle that is less than one quarter of a period of oscillation ofthe oscillating mirror and has pulses with leading edges offset from amaximum opening angle of the oscillating mirror and trailing edgesoffset from a zero crossing of the opening angle of the oscillatingmirror.

First and second samples of a mirror sense signal may be taken at nexttwo occurrences of the derivative of capacitance of the oscillatingmirror with respect to time being zero. In some cases, the first andsecond samples may instead be taken during a single mirror cycle, orduring a single period of the mirror sense signal. At least one propertyof the oscillating mirror may be determined as a function of the firstand second samples.

Also disclosed herein is a laser scanning projector including a movablemicromirror, drive circuitry configured to generate a drive signal forthe movable micromirror to thereby cause the movable micromirror to movebetween first and second set rotation limits, and a processor configuredto generate a mirror drive control signal for the drive circuitry tocause the drive circuitry to generate the drive signal so as to havepulses associated with times at which a derivative of capacitance of themovable micromirror with respect to time is zero.

The laser scanning projector may be configured to define a wafer detectscanner, laser printer, document scanner, augmented reality device, orpico-projector.

The association between the pulses and the time at which the derivativeof the capacitance of the movable micromirror with respect to time iszero may be that a rising edge of each pulse occurs an offset period oftime after each time at which the derivative of capacitance of themovable micromirror with respect to time is zero, and that a fallingedge of each pulse occurs an offset period of time before each time atwhich an opening angle of the movable micromirror is zero.

The pulses of the drive signal may be generated so as to be trapezoidalin shape.

The processor may be further configured to receive a mirror sense signalfrom the movable micromirror, take first and second samples of themirror sense signal, both samples being taken between pulses of thedrive signal, and determine at least one property of the movablemicromirror as a function of the first and second samples.

The determined at least one property may be a phase between the mirrordrive signal and the mirror sense signal.

The determined at least one property may be that the movable micromirrorhas failed.

The processor may also be configured to receive a mirror sense signalfrom the movable micromirror, take a first sample of the mirror sensesignal at a zero crossing of an opening angle of the movablemicromirror, and take a second sample of the mirror sense signal at anext occurrence of a time at which the derivative of the capacitance ofthe movable micromirror with respect to time is zero.

The processor may cause the drive circuitry to generate the drive signalso as to have the pulses transition from deasserted to asserted at anoffset period of time after each time at which the derivative of thecapacitance of the movable micromirror with respect to time is zero andan opening angle of the movable micromirror is nonzero.

The times at which a derivative of an opening angle of the movablemicromirror with respect to time is zero and the opening angle of themovable micromirror is nonzero may represent minimums of the openingangle of the movable micromirror.

The times at which a derivative of an opening angle of the movablemicromirror with respect to time is zero and the opening angle of themovable micromirror is nonzero may represent maximums of the openingangle of the movable micromirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a movable MEMS mirror such as may be usedwith the techniques described in this disclosure.

FIG. 2 is a perspective view showing operation of a movable MEMS mirrorscanning.

FIG. 3 is a graph showing the opening angle of a movable MEMS mirror vsits capacitance.

FIG. 4 is a graph showing a typical drive signal for a movable MEMSmirror overlaid with the opening angle of that movable MEMS mirror overtime.

FIG. 5 is a graph showing a typical dual drive signal for a movable MEMSmirror overlaid with the opening angle of that movable MEMS mirror overtime.

FIG. 6 is a graph showing a dual drive signal for a movable MEMS mirroroverlaid with the opening angle of that movable MEMS mirror over time,as well as acquisition points for sampling the mirror sense signal ofthat movable MEMS mirror, in accordance with techniques disclosedherein.

FIG. 7 is a schematic block diagram showing drive and control circuitryfor driving a movable MEMS mirror in accordance with a drive techniquedescribed herein.

DETAILED DESCRIPTION

One or more embodiments of the present disclosure will be describedbelow. These described embodiments are only examples of the presentlydisclosed techniques. Additionally, in an effort to provide a concisedescription, all features of an actual implementation may not bedescribed in the specification.

When introducing elements of various embodiments of the presentdisclosure, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Additionally, it should be understood that references to “oneembodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Like referencenumbers in the drawing figures refer to like elements throughout.

First, a movable MEMS mirror 100, such as may be used in devices such aswafer defect scanners, laser printers, document scanners, augmentedreality devices, projectors, and pico-projectors, will now be describedwith reference to FIG. 1. The movable MEMS mirror 100 includes a stator102 having inwardly projecting fingers 103. A rotor 104 is positionedwithin the stator 102 and has outwardly projecting fingers 105 thatinterleave with the inwardly projecting fingers 103 of the stator 102.The rotor 104 oscillates about its axis, oscillating its mirror surfacewith respect to the stator 102.

Either the stator 102 or the rotor 104 is supplied with a periodicmirror drive signal, such as a square wave, while the other is suppliedwith a reference voltage. As shown in FIG. 1, the stator 102 is suppliedwith the mirror drive signal and the rotor 104 produces a mirror sensesignal. In some cases, however, the rotor 104 may instead be suppliedwith the mirror drive signal and the stator may produce the mirror sensesignal.

In the case where the mirror drive signal has an oscillating squarevoltage, for example, electrostatic forces cause the rotor 104 tooscillate about its axis relative to the stator 102. In the case wherethe mirror drive signal has an oscillating square current, for example,magnetic forces cause the rotor 104 to oscillate about its axis relativeto the stator 102. Indeed, the movable MEMS mirror 100 may be drivenaccording to any suitable way known to those of skill in the art, suchas through the use of the piezoelectric effect or thermoelectric effect.As another example, the movable MEMS mirror 100 may be driven by drivingcurrent flow through a coil, creating an electromagnetic field used todrive the rotation of the rotor 104. Thus, it should be understood thatthe techniques, circuits, and methods described herein are applicable toany movable MEMS mirror 102, regardless of how it is driven.

For use in scanning a light beam across a surface, the movable MEMSmirror 100 is driven so that it oscillates at a frequency close to itsresonant frequency between two set or controllable oscillation limits.In some cases, the movable MEMS mirror 100 may be driven outside of itsresonance frequency, for example driven in a quasi-static or linearmode.

Shown in FIG. 2 is the movable MEMS mirror 100 scanning a light beamacross a projection screen between two set rotation limits that definean “opening angle” θ of the movable MEMS mirror 100. As can be seen inthe graphs of FIG. 3, the opening angle θ of the movable MEMS mirror 100is related to the capacitance of the movable MEMS mirror 100. Thecapacitance of the movable MEMS mirror 100 peaks when the opening angleθ is at zero, as can be seen. Thus, as can also be seen, the derivativeof capacitance of the movable MEMS mirror 100 with respect to time iszero where the opening angle θ is zero, where the opening angle θ is ata maximum, and where the opening angle θ is at a minimum.

A typical mirror drive signal is shown in FIG. 4. As can be seen, themirror drive signal is a square wave that transitions low to high, ordeasserted to asserted, at each maximum value of the opening angle θ. Asexplained above, however, this mirror drive signal has drawbacks such asthe need for a relatively high magnitude voltage.

An improved mirror drive signal is shown in FIG. 5. Here, the mirrordrive signal is a square wave that transitions low to high, ordeasserted to asserted, at each maximum, as well as each minimum, valueof the opening angle θ, making the mirror drive signal symmetric. Thisprovides for twice the duty cycle of a conventional mirror drive signal.Stated another way, the frequency of this mirror drive signal is twicethat of the opening angle θ of the movable MEMS mirror 100. Stated yetanother way, this mirror drive signal includes two pulses per eachperiod of mirror oscillation, each occurring at time when the derivativeof capacitance of the movable MEMS mirror 100 is zero. This allows forthe mirror drive signal to have a lower voltage magnitude to achieve agiven opening angle θ than required by the mirror drive signal shown inFIG. 4. This lower voltage magnitude and allows for the construction ofa more robust movable MEMS mirror 100. In addition, this provides for alonger effective application of torque to the movable MEMS mirror 100than would be applied by the mirror drive signal shown in FIG. 4. Thisalso reduces the occurrence of spurious drive modes.

However, due to the longer effective application of torque to themovable MEMS mirror 100, the available duration for sampling the mirrorsense signal 201 when it is not saturated is shorter. Therefore, afurther improved mirror drive signal shown in FIG. 6 has been developed,which will now be described together with the device 200 of FIG. 7implementing a movable MEMS mirror 100 using this mirror drive signal.The device 200 includes an analog to digital converter 202 coupled toreceive a mirror sense signal 201 from the mirror 100 and convert itinto a digital mirror sense signal 203. Control circuitry 204 receivesthe digital mirror sense signal 203 and converts it to a mirror drivecontrol signal 205. Mirror drive circuitry 206 receives the mirror drivecontrol signal 205 and generates the mirror drive signal 207 (shown inFIG. 6) from the mirror drive control signal 205.

As can be seen, this mirror drive signal 207 has pulses that are offsetfrom the maximum and minimum opening angles θ. This offset can be seenin FIG. 6 in which the offset between the leading edge of the mirrordrive signal pulses and the maximum opening angle is about 3%, and theoffset between the trailing edge of the drive pulses and the zerocrossings is about 8%. These are sample offsets, however, and otheroffsets may be used. The offsets as shown permit sampling of the mirrorsense signal 201 at a zero crossing of the opening angle θ, and at anext maximum or minimum (whichever occurs first) opening angle θ. Thatis, the rising edge of each pulse of the mirror drive signal 207 beginsan offset period of time after occurrence of a maximum or minimumopening angle θ. In addition, the shape of each pulse may betrapezoidal, thereby lowering the duty cycle compared to the rectangularpulses of the mirror drive signal 207 of FIG. 5, further increasing thesampling region. This duty cycle may be less than one quarter of aperiod of oscillation of the movable MEMS mirror 100. Moreover, it isnoted that the pulses of the mirror drive signal 207 have leading edgesoffset (after) from a maximum opening angle θ and trailing edges offset(before) from a zero crossing of the opening angle θ. This mirror drivesignal 207 is also symmetric, providing for twice the duty cycle of aconventional single pulse mirror drive signal. Stated another way, thefrequency of this mirror drive signal 207 is twice that of the openingangle θ of the movable MEMS mirror 100. Stated yet another way, thismirror drive signal 207 includes two pulses per each period of mirroroscillation, each occurring at time offset from and subsequent to whenthe derivative of capacitance of the movable MEMS mirror 100 is zero.

As stated above, the mirror sense signal 201 may be sampled at a zerocrossing of the opening angle θ, and at a next maximum or minimum(whichever occurs first) opening angle θ. In some instances, the mirrorsense signal 201 can be sampled at the next two occurrences of thederivative of capacitance of the movable MEMS mirror 100 with respect totime being zero, although the samples can also be taken at otherlocations. For example, the samples can be taken at two configuredpoints in the mirror cycle. These points are configured by a percentageof one line (i.e. half a mirror cycle). For example, in FIG. 5, thesamples can be taken at 47.3% and 97.3% (and thus there is always a 50%difference).

From these samples, the phase of the movable MEMS mirror 100 may bedetermined, and the frequency of the mirror drive control signal 205 canbe adjusted so that the mirror drive signal 207 results in a desiredphase. The desired phase is an optimal state in which the opening angleθ is at or close to a maximum value. In this state, the frequency offthe drive signal at or close to the resonance frequency of the movableMEMS mirror 100.

In addition, from the phase, it may be determined that the movable MEMSmirror 100 has failed, and an appropriate flag may be set for use byother circuitry, for example to switch off a laser impinging onto themovable MEMS mirror 100.

While the disclosure has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be envisionedthat do not depart from the scope of the disclosure as disclosed herein.Accordingly, the scope of the disclosure shall be limited only by theattached claims.

1. A device, comprising: mirror control circuitry configured to control a movable mirror, wherein the mirror control circuitry comprises: drive circuitry configured to provide a drive signal to the movable mirror; and a processor configured to: cause the drive circuitry to generate the drive signal so as to have pulses associated with times at which a derivative of capacitance of the movable mirror with respect to time is zero.
 2. The device of claim 1, wherein said times at which the derivative of the capacitance of the movable mirror with respect to time is zero comprise a rising edge of each pulse that occurs an offset period of time after each time at which the derivative of capacitance of the movable mirror with respect to time is zero but an opening angle of the movable mirror is nonzero, and that a falling edge of each pulse occurs an offset period of time before each time at which the opening angle of the movable mirror is zero.
 3. The device of claim 1, wherein the drive signal generates pulses of the drive signal that are trapezoidal in shape.
 4. The device of claim 1, wherein the processor is further configured to: receive a mirror sense signal from the movable mirror; take first and second samples of the mirror sense signal, both samples being taken between pulses of the drive signal; determine at least one property of the movable mirror as a function of the first and second samples; and perform an action based upon the determined at least one property.
 5. The device of claim 4, wherein the determined at least one property is a phase between the mirror drive signal and the mirror sense signal; and wherein the action performed is to adjust the drive circuitry such that the phase matches a desired phase.
 6. The device of claim 4, wherein the determined at least one property is that the movable mirror has failed; and wherein the action performed is to generate a flag indicating that the mirror has failed.
 7. The device of claim 1, wherein the processor is configured to: receive a mirror sense signal from the movable mirror; take a first sample of the mirror sense signal at a zero crossing of an opening angle of the movable mirror; take a second sample of the mirror sense signal at a next occurrence of a time at which the derivative of the capacitance of the movable mirror with respect to time is zero; perform an action based upon the determined at least one property.
 8. The device of claim 1, wherein the processor causes the drive circuitry to generate the drive signal so as to have pulses which transition from deasserted to asserted at an offset period of time after each time at which the derivative of the capacitance of the movable mirror with respect to time is zero and an opening angle of the movable mirror is nonzero.
 9. The device of claim 1, wherein the times at which a derivative of an opening angle of the movable mirror with respect to time is zero and an opening angle of the movable mirror is nonzero represent maximums or minimums of the opening angle of the movable mirror.
 10. The device of claim 1, wherein the movable mirror comprises an oscillating micromirror.
 11. A device, comprising: mirror control circuitry configured to control a movable mirror, the mirror control circuitry comprising: drive circuitry configured to provide a drive signal to the movable mirror; and a processor configured to cause the drive circuitry to generate the drive signal having a frequency that is twice a frequency of oscillation of the movable mirror but does not have pulses occurring at times at which a derivative of capacitance of the movable mirror with respect to time is zero.
 12. The device of claim 11, wherein the processor is further configured to: receive a mirror sense signal from the movable mirror; and take first and second samples of the mirror sense signal at next two occurrences of the derivative of capacitance of the movable mirror with respect to time being zero.
 13. A device, comprising: mirror control circuitry configured to control an oscillating mirror, wherein the mirror control circuitry comprises: drive circuitry configured to provide a drive signal to the oscillating mirror; and a processor configured to cause the drive circuitry to generate the drive signal so as to have a duty cycle that is less than one quarter of a period of oscillation of the oscillating mirror and has pulses with leading edges offset from a maximum opening angle of the oscillating mirror and trailing edges offset from a zero crossing of the opening angle of the oscillating mirror.
 14. The device of claim 13, wherein the processor is further configured to: receive a mirror sense signal from the oscillating mirror; and take first and second samples of the mirror sense signal at next two occurrences of a derivative of capacitance of the oscillating mirror with respect to time being zero.
 15. A method, comprising: generating a drive signal for an oscillating mirror; and wherein the drive signal is generated to have a duty cycle that is less than one quarter of a period of oscillation of the oscillating mirror and has pulses with leading edges offset from a maximum opening angle of the oscillating mirror and trailing edges offset from a zero crossing of an opening angle of the oscillating mirror.
 16. The method of claim 15, further comprising taking first and second samples of a mirror sense signal at next two occurrences of a derivative of capacitance of the oscillating mirror with respect to time being zero.
 17. The method of claim 16, further comprising determining at least one property of the oscillating mirror as a function of the first and second samples.
 18. A laser scanning projector, comprising: a movable micromirror; drive circuitry configured to generate a drive signal for the movable micromirror to thereby cause the movable micromirror to move between first and second set rotation limits; and a processor configured to generate a mirror drive control signal for the drive circuitry to cause the drive circuitry to generate the drive signal so as to have pulses associated with times at which a derivative of capacitance of the movable micromirror with respect to time is zero.
 19. The laser scanning projector of claim 18, wherein the laser scanning projector is configured to define a wafer detect scanner, laser printer, document scanner, augmented reality device, or pico-projector.
 20. The laser scanning projector of claim 18, wherein the association between the pulses and the time at which the derivative of the capacitance of the movable micromirror with respect to time is zero is that a rising edge of each pulse occurs an offset period of time after each time at which the derivative of capacitance of the movable micromirror with respect to time is zero, and that a falling edge of each pulse occurs an offset period of time before each time at which an opening angle of the movable micromirror is zero.
 21. The laser scanning projector of claim 18, wherein the pulses of the drive signal are generated so as to be trapezoidal in shape.
 22. The laser scanning projector of claim 18, wherein the processor is further configured to: receive a mirror sense signal from the movable micromirror; take first and second samples of the mirror sense signal, both samples being taken between pulses of the drive signal; and determine at least one property of the movable micromirror as a function of the first and second samples.
 23. The laser scanning projector of claim 22, wherein the determined at least one property is a phase between the mirror drive signal and the mirror sense signal.
 24. The laser scanning projector of claim 22, wherein the determined at least one property is that the movable micromirror has failed.
 25. The laser scanning projector of claim 18, wherein the processor is configured to: receive a mirror sense signal from the movable micromirror; take a first sample of the mirror sense signal at a zero crossing of an opening angle of the movable micromirror; and take a second sample of the mirror sense signal at a next occurrence of a time at which the derivative of the capacitance of the movable micromirror with respect to time is zero.
 26. The laser scanning projector of claim 18, wherein the processor causes the drive circuitry to generate the drive signal so as to have the pulses transition from deasserted to asserted at an offset period of time after each time at which the derivative of the capacitance of the movable micromirror with respect to time is zero and an opening angle of the movable micromirror is nonzero.
 27. The laser scanning projector of claim 18, wherein the times at which a derivative of an opening angle of the movable micromirror with respect to time is zero and the opening angle of the movable micromirror is nonzero represent minimums of the opening angle of the movable micromirror.
 28. The laser scanning projector of claim 18, wherein the times at which a derivative of an opening angle of the movable micromirror with respect to time is zero and the opening angle of the movable micromirror is nonzero represent maximums of the opening angle of the movable micromirror. 